Absorbent members for body fluids using hydrogel-forming absorbent polymer

ABSTRACT

Absorbent members useful in the containment of body fluids such as urine, that have at least one region containing hydrogel-forming absorbent polymer in a concentration of from about 50 to 100% by weight and providing a gel-continuous fluid transportation zone when in a swollen state. This hydrogel-forming absorbent polymer has: (a) a Dynamic Gelling Rate of at least about 0.18 g/g/sec; (b) a Performance under Pressure (PUP) capacity value of at least about 25 g/g under a confining pressure of 0.7 psi (5 kPa); and (c) when the hydrogel-forming absorbent polymer is in the form of particles, a mass median particle size of at least about 100 μm.

This application is a 371 of PCT/IB98/00537 filed Apr. 9, 1998 whichclaims benefit of Provisional No. 60/044,628 filed Apr. 18, 1997.

TECHNICAL FIELD

This application relates to absorbent members having at least one regionwith a relatively high concentration of hydrogel-forming absorbentpolymer having specific rates of gellation and absorbency performanceunder pressure.

BACKGROUND OF THE INVENTION

The development of highly absorbent members for use as disposablediapers, adult incontinence pads and briefs, and catamenial productssuch as sanitary napkins, is the subject of substantial commercialinterest. A highly desired characteristic for such products is thinness.Thinner products are less bulky to wear, fit better under clothing, andare less noticeable. They are also more compact in the package, makingthe products easier for the consumer to carry and store. Smallerproducts allow reduced distribution costs for the manufacturer anddistributor, require less shelf space required in the store per diaperunit, and require less packaging material.

The ability to provide thinner absorbent articles such as diapers iscontingent on the ability to develop relatively thin absorbent cores orstructures that can acquire and store large quantities of dischargedbody fluids such as urine or menses. In this regard, the use of certainabsorbent polymers often referred to as “hydrogels,” “superabsorbents”or “hydrocolloid” material has been particularly important. See, forexample, U.S. Pat. No. 3,699,103 (Harper et al.), issued Jun. 13, 1972,and U.S. Pat. No. 3,770,731 (Harmon), issued Jun. 20, 1972, thatdisclose the use of such absorbent polymers (hereafter “hydrogel-formingabsorbent polymers”, or HFAPs) in absorbent articles. Indeed, thedevelopment of thinner products has been the direct consequence ofthinner absorbent cores that take advantage of the ability of thesehydrogel-forming absorbent polymers to absorb large quantities ofdischarged body fluids, typically when used in combination with afibrous matrix as compared with a fibrous matrix alone. See, forexample, U.S. Pat. No. 4,673,402 (Weisman et al.), issued Jun. 16, 1987and U.S. Pat. No. 4,935,022 (Lash et al.), issued Jun. 19, 1990, thatdisclose dual-layer core structures comprising a fibrous matrix andhydrogel-forming absorbent polymers useful in fashioning thin, compact,products.

Significant prior art describes absorbent structures having relativelylow amounts (e.g., less than about 50% by weight) of thesehydrogel-forming absorbent polymers. See, for example, U.S. Pat. No.4,834,735 (Alemany et al.), issued May 30, 1989 (preferably from about 9to about 50% hydrogel-forming absorbent polymer in the fibrous matrix).There are several reasons for this. The hydrogel-forming absorbentpolymers employed in prior absorbent structures have generally not hadan absorption rate that would allow them to quickly absorb body fluids,especially in “gush” situations. This has necessitated the inclusion offibers, typically wood pulp fibers, to serve as temporary reservoirs tohold the discharged fluids until absorbed by the hydrogel-formingabsorbent polymer. This fluid is not tightly held in storage cores andcan be expressed by pressure or capillary contact back onto the skin ofthe wearer, resulting in undesirable skin wetness. In order to maintainskin dryness, such fluid must be gelled quickly and completely. Also,cores made with relatively low concentrations of HFAP are inherentlyrelatively thick and bulky.

HFAPs are often made by polymerizing unsaturated carboxylic acids orderivatives thereof, such as acrylic acid or its salt with low levels ofcrosslinking monomers, typically di- or poly-functional monomermaterials such as N, N′-methylenebisacrylamide, trimethylol propanetriacrylate, or triallyl amine. The presence of crosslinking monomersrenders these polymers water-insoluble, yet water-swellable. Higherlevels of cross-linking increase gel strength while reducing gelvolumes. Gel strength relates to the tendency of the hydrogel formedfrom these polymers to deform or “flow” under an applied stress. Gelstrength needs to be such that the hydrogel formed does not deform andfill to an unacceptable degree the capillary void spaces in theabsorbent structure or article, a phenomenon called “gel blocking”. Thiswould otherwise reduce the rate of absorption and the fluid distributionthroughout the structure/article. Various designs have been advocatedfor reducing or preventing gel blocking, some of which require use ofadded fibrous material which tends to increase the thickness of theproduct undesirably. See, for example, U.S. Pat. No. 4,654,039 (Brandtet al.), issued Mar. 31, 1987 (reissued Apr. 19, 1988 as U.S. ReissuePat. No. 32,649), U.S. Pat. No. 4,834,735 (Alemany et al.), issued May30, 1989. U.S. Pat. No. 5,652,646 (Goldman et al.), issued Oct. 8, 1996,describes use of HFAPs which have both high porosity and high strengthin high concentration cores. This patent therefore addresses the problemof gel blocking in high concentration HFAP regions by using HFAPs thatretain porosity such that additional fibers are not necessary.

The effective rate at which these hydrogel-forming polymers will gel inthe presence of body fluids (e.g., urine) is also important. A typicalcurrent hydrogel-forming polymer will gel completely when exposed toexcess aqueous fluids such as urine over a period of about 5-20 minutes.

The rate of gellation of HFAPs in aqueous fluids has been measured byseveral techniques. The vortex method described in U.S. Pat. No.5,601,542 involves addition of HFAP to a stirring aqueous solution andmeasuring the time required for the solution to seize and stop stirring.This patent describes absorbent cores having concentrations of HFAP of30-100% which also have a Pressure Absorbency Index (PAI) (a value saidto relate to insensitivity to pressure, infra) of at least 120 andextractables levels of less than about 13 wt. percent. Claim 29 of thispatent describes similar high concentration cores made with HFAPS havinga PAI of at least 120 and a vortex time of less than about 45 seconds.

The Free Swell Rate (FSR) method described in U.S. Pat. No. 5,149,335(Kellenberger et al.) issued Sep. 22, 1992 involves determination of thetime required for 1.0 g of HFAP to imbibe 20 mL of test fluid.

Yet another method involves microscopic examination of the HFAP in thegelling solution and measuring the dimensions at specific time intervals(Tanaka, T.; Fillmore, D. J. J. Chem. Phys., 1979, 70, 1214).

Still another method involves spectrophotometric monitoring of a dyewhich is excluded from the gel in excess aqueous solution which becomesconcentrated as the gel expands, as described in a Diploma Thesis byHerbert Heitmann, Universitat Dortmund Lehrstuhl fur ThermischeVerfahrenstechnik, August 1989.

Each of these methods suffers from certain deficiencies. The vortexmethod has a subjective end point. This end point may also be undulyinfluenced by the presence of high molecular weight extractablecomponents which can prematurely thicken the solution. The FSR methodand the vortex method do not distinguish between fluid which is actuallygelled and fluid which is loosely held interstitially, and thus can beeasily expressed by pressure or capillary contact back onto the skin ofthe wearer. It is believed that a substantial fraction of the fluid(e.g., on the order of about 50% or more) at the FSR endpoint is heldinterstitially. It is further believed that the fraction of fluid heldinterstitially at the FSR endpoint will vary depending on particlemorphology. Also, the FSR method is not usable for HFAPs which absorbthe fluid very quickly as the apparent fluid uptake is achieved beforeall of the HFAP used in the test is wetted. The FSR method, like thevortex method, has an imprecise endpoint, which is particularly criticalfor very fast HFAPs. The spectrophotometric method, as described above,is not quickly responsive to changes in gel volume. Such a quickresponse requires minimal lag time between sampling and the reading ofoptical absorbency. This obviously becomes important for very fastHFAPs. Also, this method does not filter out floating pieces of smallmaterial generated during stirring which tend to interfere with thelight path.

Applicants have modified the spectrophotometric method to provide dataon the actual rate of gellation critical to the performance of anabsorbent product. This was achieved by shortening the sampling pathlength to shorten the time between the actual change in opticalabsorbency and the spectrophotometric response to that change. Further,a self-cleaning filtration assembly was added to exclude particulatematerials which can interfere with the light path. Unlike the vortexmethod supra, Applicants' approach is not sensitive to extractablematerials which may thicken the solution (but which do not change theoptical absorbency of the solution). Unlike the vortex method and theFree Swell Rate method (supra), this modified method has a specific endpoint independent of operator judgment. Unlike the Free Swell and Vortexmethods, this method does not measure trapped interstial fluid. Unlikethe Free Swell Rate method (supra), this method is also usable for veryfast HFAPs useful in the present invention.

The data obtained initially show optical absorbency which is simplyconverted into gel volume as a function of elapsed time. The data curvesshowing gel volume vs. elapsed time can be fit using a simplelogarithmic expression defined hereinafter. This allows unambiguousexpression of the gelling curve using a single value, referred to hereinas the Dynamic Gelling Rate, or DGR, in units of g/g/sec. HFAPs whichexhibit faster rates without compromising other properties unacceptablyhave been found to be particularly preferred in specific types ofabsorbent core designs, described in detail hereinafter.

It has been generally recognized as desirable to have the expressedfluid converted into the gelled state as rapidly as possible. Forexample, U.S. Pat. No. 5,439,458 (Noel et al.) issued Aug. 8, 1995describes absorbent articles with a “rapid acquiring, multiple layerabsorbent core” using a ““high-speed” absorbent gelling material capableof reaching at least 40% of its absorbent capacity in less than or equalto about 10 seconds.” U.S. Pat. No. 5,300,054 (Feist et al.) issued Apr.5, 1994 describes absorbent cores having storage layers at leastpartially comprising high speed absorbent gelling material. High speedHFAPs generally have been disclosed. For example, U.S. Pat. No.5,563,218 (Rebre et al.) issued Oct. 8, 1996 discloses a process forproducing “high gel strength/short gel time acrylic polymers”. U.S. Pat.No. 5,601,542 (Melius et al.) issued Feb. 11, 1997 describes absorbentcomposites having specified vortex times and demand gel volumes underpressure (infra). U.S. Pat. No. 5,149,335 (Kellenberger et al.) issuedSep. 22, 1992 describes use of superabsorbent material at least 15 g/gAbsorbency Under Load (AUL) (infra) after 5 minutes and a Free SwellRate of less than about 60 seconds.

U.S. Pat. No. 5,354,290 (Gross) issued Oct. 11, 1994 and U.S. Pat. No.5,403,870 (Gross) issued Apr. 4, 1995 describe a method for producingporous HFAPs with high absorbent rates. U.S. Pat. No. 5,154,713 (Lind)issued Oct. 13, 1992, U.S. Pat. No. 4,649,164 (Scott et al.) issued Mar.10, 1987, U.S. Pat. No. 4,529,739 (Scott et al.) issued Jul. 16, 1985,U.S. Pat. Nos. 5,154,714, and 5,399,591 describe inclusion of carbonateblowing agents in the HFAP manufacturing process to increase internaland external surface area and increase absorbent rates. World Patent95/17,455 describes porous superabsorbents with high absorption ratesgenerated by use of nitrogen generating initiators during thepolymerization. World Patent Publication WO 96/17,884 published June,1996, describes dispersal of solid blowing agent in the aqueous solutionof monomer and crosslinker followed by heating to polymerize into aporous structure with a high rate of water absorption. The disclosure ofthis publication is incorporated herein by reference.

In some cases, use of high concentrations of fast HFAPs, particularly inthe loading zone of the absorbent core, can actually impair fluidsorption rates. This is believed to result from rapid gellation of theHFAP with attendant tendencies to reduce porosity and/or permeability,and even gel block, and thus reduce the ability of the absorbent core toaccommodate repeat insults of the body fluid. In such cases, it can bedesirable to employ HFAPs with particularly high porosities and/orpermeabilities so as to avoid this problem. Alternatively, a mixture ofHFAP types can be employed wherein at least part of the HFAP blend has avery high rate of fluid uptake and porosity and/or permeability.

Other physical and chemical characteristics of these hydrogel-formingabsorbent polymers are important to performance in absorbent structures.One characteristic is the particle size, and especially the particlesize distribution, of the hydrogel-forming absorbent polymer used in thefibrous matrix. For example, particles of hydrogel-forming absorbentpolymer having a particle size distribution such that the particles havea mass median particle size greater than or equal to about 400 μm havebeen mixed with hydrophilic fibrous materials to minimize gel blockingand to help maintain an open capillary structure within the absorbentstructure so as to enhance planar transport of fluids away from the areaof initial discharge to the rest of the absorbent structure. Such largerparticles tend to be relatively slow to imbibe aqueous fluids. Whilesmaller particles of HFAP will generally show faster rates of gellation,this can also lead to depressed gel volumes (when surface crosslinker,infra) and/or gel blocking as a result of such small particles. Smallparticles in the dry state can also be difficult to handle inmanufacturing due to problems with respirable dust. Small particles inthis discussion refers to generally (compact) spherical (e.g., notcylindrical as is a fiber) materials which have a maximumcross-sectional dimension of about 100 μm. Small particles, also calledfines, may also be reformed into aggregates or agglomerates byadditional processing (or by methods of preparation; e.g., suspensionpolymerization). This can minimize some of the problems associated withuse of fines. However, the additional processing step can be problematicand expensive. Also, the agglomerated particles tend not to be stableduring processing and usage and often release significant quantities offines back into the absorbent product. Accordingly, it is preferred thatthe HFAPs useful herein not be in the form of agglomerated particles.That is, unagglomerated HFAPs are preferred herein. (FIG. 5 illustratesunagglomerated HFAP particles useful herein). Hydrogel-forming absorbentpolymers useful herein can be derived from fines by impregnation withadditional monomer to build up their size as described in U.S. Pat. No.5,514,574 (Henderson et al.), issued May 7, 1996. U.S. Pat. No.5,122,544 (Bailey et al.) issued Jun. 16, 1992 describes a process foragglomerating gel fines using difunctional epoxides. U.S. Pat. No.4,950,692 (Lewis et al.) issued Aug. 21, 1990 and U.S. Pat. No.4,970,267 (Bailey et al.) issued Nov. 13, 1990 similarly describeagglomeration of gel fines. U.S. Pat. No. 5,384,343 describes a processfor agglomeration of fines (<50 μm into larger particles of 50-500 μm).U.S. Pat. No. 5,369,148 (Takahashi et al.) issued Nov. 29, 1994describes a method of agglomeration of absorbent resin powder. U.S. Pat.No. 5,455,284 (Dahmen et al.) issued Oct. 3, 1995 describes recyclingfines into more monomer from which a new HFAP may be formed viapolymerization. U.S. Pat. No. 5,248,709 (Brehm) issued Sep. 28, 1993describes a method for sinter granulation of fines. U.S. Pat. No.5,350,799 (Woodrum et al.) issued Sep. 27, 1994 describes yet anotherprocess for converting fines into large particles. French Patent2,732,973 issued October 1996, describes a process to provide a goodyield of aggregated particles without fines. The above references areincorporated herein by reference.

Another important characteristic is particle size distribution of thehydrogel-forming absorbent polymer. This can be controlled to improveabsorbent capacity and efficiency of the particles employed in theabsorbent structure. See U.S. Pat. No. 5,047,023 (Berg), issued Sep. 10,1991, and U.S. Pat. No. 5,397,845 (Rebre et al.) issued Mar. 14, 1995and U.S. Pat. No. 5,412,037 (Rebre et al.) issued May 2, 1995 describingHFAPs with a narrow particle size distribution between 100 and 500 μmessentially devoid of fines. However, even adjusting the particle sizedistribution does not, by itself, lead to absorbent structures that canhave relatively high concentrations of these hydrogel-forming absorbentpolymers. See U.S. Pat. No. 5,047,023, supra (optimum fiber to particleratio on cost/performance basis is from about 75:25 to about 90:10).

Another characteristic of these hydrogel-forming absorbent polymers thathas been looked at is the level of extractables present in the polymeritself. See U.S. Pat. No. 4,654,039 (Brandt et al.), issued Mar. 31,1987 (reissued Apr. 19, 1988 as U.S. Reissue Pat. No. 32,649). Many ofthese hydrogel-forming absorbent polymers contain significant levels ofextractable polymer material. This extractable polymer material can beleached out from the resultant hydrogel by body fluids (e.g., urine)during the time period such body fluids remain in contact with thehydrogel-forming absorbent polymer. Such polymer material extracted bybody fluid in this manner can alter the properties, e.g., increaseviscosity and also electrolyte concentration of the body fluid to theextent that the fluid is more slowly absorbed and more poorly held bythe hydrogel in the absorbent article.

Another important characteristic is the capillary capability of thesehydrogel-forming absorbent polymers. In particular, it has beensuggested that particles of these hydrogel-forming absorbent polymers beformed into interparticle crosslinked aggregate macrostructures,typically in the form of sheets or strips. See U.S. Pat. No. 5,102,597(Roe et al.), issued Apr. 7, 1992; U.S. Pat. No. 5,124,188 (Roe et al.),issued Jun. 23, 1992; and U.S. Pat. No. 5,149,344 (Lahrman et al.),issued Sep. 22, 1992. Because the particulate nature of the absorbentpolymer is retained, these macrostructures provide pores betweenadjacent particles that are interconnected such that the macrostructureis fluid permeable (i.e., has capillary transport channels).

Another important characteristic is gel blocking as measured in a DemandWettability or Gravimetric Absorbence test. See, for example, U.S. Pat.No. 5,147,343 (Kellenberger), issued Sep. 15, 1992 and U.S. Pat. No.5,149,335 (Kellenberger et al.), issued Sep. 22, 1992 where thesehydrogel-forming absorbent polymers are referred to as “superabsorbentmaterials” and where Demand Wettability/Gravimetric Absorbence isreferred to as Absorbency Under Load (AUL). “AUL” is defined in thesepatents as the ability of the hydrogel-forming absorbent polymer toswell against an applied restraining force (see U.S. Pat. No. 5,147,343,supra, at Col. 2, lines 43-46). The “AUL value” is defined as the amount(in mL/g or g/g) of 0.9% saline solution that is absorbed by thehydrogel-forming absorbent polymers while being subjected to a load of21,000 dynes/cm² (about 0.3 psi). The AUL value can be reported after 1hour (see U.S. Pat. No. 5,147,343) or 5 minutes (see U.S. Pat. No.5,149,335). Hydrogel-forming absorbent polymers are deemed to havedesirable AUL properties if they absorb at least about 24 mL/g(preferably at least about 27 mL/g) of the saline solution after 1 hour(see U.S. Pat. No. 5,147,343) or at least about 15 g/g (preferably atleast about 18 g/g) of the saline solution after 5 minutes.

AUL as defined in U.S. Pat. Nos. 5,147,343 and 5,149,335 may providesome indication of which hydrogel-forming absorbent polymers will avoidgel blocking in some instances. However, AUL does not specificallydetermine rate of gelling or distinguish between moderately fast andvery fast absorbing HFAPs. Further, AUL is inadequate for determiningwhich hydrogel-forming absorbent polymers will provide the absorbencyproperties necessary for high concentration absorbent cores, as isdescribed in U.S. Pat. No. 5,599,335 (supra). In particular, using AULvalues measured according to U.S. Pat. Nos. 5,147,343 and 5,149,335 isinadequate in that they do not reflect all of the potential pressuresthat can be operative on the hydrogel-forming polymer in the absorbentstructure. As noted above, AUL is measured in these patents at apressure of about 0.3 psi. It is believed that a much higher confiningpressure of about 0.7 psi more adequately reflects the full range oflocalized mechanical pressures (e.g., sitting, sleeping, squatting,taping, elastics, leg motions, other tension and torsional motions) onan absorbent structure. See U.S. Pat. No. 5,147,345 (Young et al),issued Sep. 15, 1992. Additionally, many of the absorbent structuresthat comprise these hydrogel-forming absorbent polymers can includeother components, such as an acquisition layer that receives the initialdischarge of body fluids. See, for example, U.S. Pat. No. 4,673,402(Weisman et al), issued Jun. 16, 1987 and U.S. Pat. No. 4,935,022 (Lashet al), issued Jun. 19, 1990. This acquisition layer can comprisefibers, such as certain chemically stiffened fibers, that have arelatively high capillary suction. See, for example, U.S. Pat. No.5,217,445 (Young et al), issued Jun. 8, 1993. To take into account theseadditional capillary pressures that could affect fluid acquisition bythese hydrogel-forming absorbent polymers, it is more realistic tomeasure demand absorbency performance under a higher pressure, i.e.,about 0.7 psi. This takes into better account not only the localizedmechanical pressures exerted during use, but also the additionalcapillary pressures resulting from other components (e.g., acquisitionlayer) present in the absorbent structure. See U.S. Pat. No. 5,599,335(Goldman et al.), which incorporated by reference herein, whichdescribes a means for measuring demand absorbency under such higherpressures.

Pressure Absorbency Index (PAI) is defined in U.S. Pat. No. 5,601,542(issued Feb. 11, 1997) Melius et al. as the sum of the AUL valuesdetermined at four pressures (0.01 psi, 0.29 psi, 0.57 psi, and 0.90psi). This is another way of presenting AUL data as an aggregate toinclude the effects of pressure on AUL.

Still other characteristics for absorbent structures having relativelyhigh concentrations of these hydrogel-forming absorbent polymers havebeen evaluated. See, for example, European patent application 532,002(Byerly et al.), published Mar. 17, 1993, which identifies acharacteristic called Deformation Under Load (DUL) as being importantfor absorbent composites having high concentrations of hydrogel-formingabsorbent polymers. “DUL” is used in European patent application 532,002to evaluate the ability of the hydrogel-forming absorbent polymer tomaintain wicking channels after the absorbent polymer is swollen. Seepage 3, lines 9-10. Further discussion of the DUL method may be found inU.S. Pat. No. 5,562,646 (supra). U.S. Pat. No. 5,562,646 describeshydrogel-forming absorbent polymers having higher porosities that areparticularly suitable for absorbent structures having highconcentrations of these absorbent polymers. The openness or porosity ofa hydrogel layer formed from a hydrogel-forming absorbent polymer can bedefined in terms of Porosity of the Hydrogel Layer (PHL). A good exampleof a material having a very-high degree openness is an air-laid web ofwood-pulp fibers. For example, the fractional degree of openness of anair-laid web of wood pulp fibers (e.g., having a density of 0.15 g/cc)is estimated to be 0.8-0.9, when wetted with body fluids under aconfining pressure of 0.3 psi. By contrast, typical hydrogel-formingpolymers such as Nalco 1180 (made by Nalco Chemical Co.) and L-761f(made by Nippon Shokubai Co., LTD) exhibit PHL values of about 0.1 orless

U.S. Pat. No. 5,562,646 teaches that higher PHL values for thehydrogel-forming absorbent polymer can provide benefits in highconcentration cores including (1) increased void volume in the resultanthydrogel layer for acquiring and distributing fluid; (2) increased totalquantity of fluid absorbed by the absorbent polymer under demandwettability/gravimetric absorbency conditions (i.e., for the storage offluid); (3) increased permeability of the resultant hydrogel layer foracquiring and distributing fluid; (4) improved wicking properties forthe resultant hydrogel layer, such as wicking fluid upwardly againstgravitational pressures or partitioning fluid away from an acquisitionlayer; and (5) improved swelling-rate properties for the resultanthydrogel layer to allow more-rapid storage of fluid.

U.S. Pat. No. 5,599,335 teaches the importance in cores having higherconcentrations of these hydrogel-forming absorbent polymers is theirpermeability/flow conductivity. Permeability/flow conductivity can bedefined in terms of their Saline Flow Conductivity (SFC) values. SFCmeasures the ability of a material to transport saline fluids, such asthe ability of the hydrogel layer formed from the swollenhydrogel-forming absorbent polymer to transport body fluids. Typically,an air-laid web of pulp fibers (e.g., having a density of 0.15 g/cc)will exhibit an SFC value of about 200×10⁻⁷ cm³sec/g. By contrast,typical hydrogel-forming absorbent polymers such as Aqualic L-74 (madeby Nippon Shokubai Co., LTD) and Nalco-1180 (made by Nalco Chemical Co.)exhibit SFC values of generally less than 1×10⁻⁷ cm³sec/g. Accordingly,it would be highly desirable to be able to use hydrogel-formingabsorbent polymers that more closely approach an air-laid web of woodpulp fibers in terms of SFC. HFAPs having relatively high SFC values areparticularly important wherein the relatively fast HFAPs of the presentinvention are used in the loading zone in high concentrations.

It is obvious from this discussion that no single parameter associatedwith HFAPs can be defined or measured to describe the suitability of agiven HFAP for a given high concentration absorbent core design.Heretofore unrecognized is the importance of rate of gellation of theHFAP in concert with their ability to absorb fluid against a confiningpressure.

Accordingly, it would be desirable to be able to provide an absorbentmember comprising: (1) a region or regions having a relatively highconcentration of hydrogel-forming absorbent polymer; (2) using HFAPswith very fast rates of gellation; (3) with relatively large particlesizes or fiber sizes; (4) that can readily acquire fluids under typicalusage pressures (e.g., 0.7 psi); preferably (5) with relatively highporosities, especially when used in the loading zone, and preferably (6)permeability/flow conductivity properties more like an air-laid fibrousweb.

SUMMARY OF THE INVENTION

The present invention relates to absorbent members useful in thecontainment of body fluids such as urine and blood. These absorbentmembers comprise at least one region having hydrogel-forming absorbentpolymer in a concentration of from about 50 to 100% by weight. Thishydrogel-forming absorbent polymer has:

(a) a Performance under Pressure (PUP) capacity value of at least about25 g/g under a confining pressure of 0.7 psi (5 kPa);

(b) a Dynamic Gelling Rate (DGR) value of at least about 0.18 g/g/sec;and

(c) when the hydrogel-forming absorbent polymer is in the form ofparticles, a mass median particle size of at least about 100 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an apparatus for measuring the DynamicGelling Rate (DGR) of hydrogel-forming absorbent polymers.

FIG. 2a is a schematic view of the self-cleaning filtering device aspectof the DGR apparatus shown in FIG. 1.

FIG. 2b is a schematic view of the filtering device depicted in FIG. 2a,but with the screen and vane removed.

FIG. 3 is a top view of the hemispherical mixing chamber aspect of theDGR apparatus shown in FIG. 1.

FIG. 4a is a close-up view of the sampling adapter aspect of the DGRapparatus shown in FIG. 1.

FIG. 4b is a close-up view of the probe holder aspect of the DGRapparatus shown in FIG. 1.

FIG. 4c is a close-up view of the fiberoptic probe aspect of the DGRapparatus shown in FIG. 1.

FIG. 5 is a scanning electron micrograph (SEM; 30X) of HFAP particles ofthe useful in the absorbent members of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to absorbent members useful in thecontainment of body fluids such as urine and blood. These absorbentmembers comprise at least one region having hydrogel-forming absorbentpolymer in a concentration of from about 50 to 100% by weight thatpreferably provides a gel-continuous fluid transportation zone when in aswollen state. This hydrogel-forming absorbent polymer has:

(a) a Performance under Pressure (PUP) capacity value of at least about25 g/g under a confining pressure of 0.7 psi (5 kPa);

(b) a Dynamic Gelling Rate (DGR) value of at least about 0.18 g/g/sec;

(c) when the hydrogel-forming absorbent polymer is in the form ofparticles, a mass median particle size of at least about 100 μm; and

(d) preferably, a Saline Flow Conductivity (SFC) value of at least about30×10⁻⁷ cm³sec/g.

A. Definitions

The following terms used herein are defined below:

“body fluids” includes urine, menses, blood, sweat, saliva, nasalmucous, and vaginal discharges.

“Z-dimension” refers to the dimension orthogonal to the length and widthof the member, core or article. The Z-dimension usually corresponds tothe thickness of the member, core or article.

“X-Y dimension” refers to the plane orthogonal to the thickness of themember, core or article. The X-Y dimension usually corresponds to thelength and width of the member, core or article.

“absorbent core” refers to the component of the absorbent article thatis primarily responsible for fluid handling properties of the article,including acquiring, transporting, distributing and storing body fluids.As such, the absorbent core typically does not include the topsheet orbacksheet of the absorbent article.

“absorbent member” refers to the components of the absorbent core thattypically provide one or more fluid handling properties, e.g., fluidacquisition, fluid distribution, fluid transportation, fluid storage,etc. The absorbent member can comprise the entire absorbent core or onlya portion of the absorbent core, i.e., the absorbent core can compriseone or more absorbent members.

“region(s)” or “zone(s)” refer to portions or sections of the absorbentmember.

“loading zone” means the region within the absorbent core which isimpacted initially by voiding of the body fluid.

“storage zone” means an area distant from the loading zone into whichthe fluid is to be permanently held. “Distant” can be in either the X-Yor Z dimensions.

“porosity” means the fractional volume (dimension-less) that is notoccupied by solid material and/or gel.

“layer” refers to an absorbent member whose primary dimension is X-Y,i.e., along its length and width. It should be understood that the termlayer is not necessarily limited to single layers or sheets of material.Thus the layer can comprise laminates or combinations of several sheetsor webs of the requisite type of materials. Accordingly, the term“layer” includes the terms “layers” and “layered.”

“comprising” means various components, members, steps and the like canbe conjointly employed according to the present invention. Accordingly,the term “comprising” encompasses the more restrictive terms “consistingessentially of” and “consisting of,” these latter, more restrictiveterms having their standard meaning as understood in the art.

For purposes of this invention, it should also be understood that theterm “upper” refers to absorbent members, such as layers, that arenearest to the wearer of the absorbent article, and typically face thetopsheet of an absorbent article; conversely, the term “lower” refers toabsorbent members that are furthermost away from the wearer of theabsorbent article and typically face the backsheet.

All percentages, ratios and proportions used herein are by weight unlessotherwise specified.

B. Material and Components of the Absorbent Member

1. Hydrogel Forming Absorbent Polymers

a. Chemical Composition

The hydrogel-forming absorbent polymers useful in the present inventioninclude a variety of water-insoluble, but water-swellable polymerscapable of absorbing large quantities of fluids. Such polymers materialsare also commonly referred to as “hydrocolloids, in. or “superabsorbent”materials and can include polysaccharides such as carboxymethyl starch,carboxymethyl cellulose, and hydroxypropyl cellulose; nonionic typessuch as polyvinyl alcohol, and polyvinyl ethers; cationic types such aspolyvinyl pyridine, and N,N-dimethylaminoethyl or N,N-diethylaminopropylacrylates and methacrylates, and the respective quaternary saltsthereof. Typically, hydrogel-forming absorbent polymers useful in thepresent invention have a multiplicity of anionic, functional groups,such as metal sulfonate and carboxylate groups. Examples of polymerssuitable for use herein include those which are prepared frompolymerizable, unsaturated, acid-containing monomers. These monomers canbe selected from olefinically unsaturated carboxylic and sulfonic acidsand acid anhydrides, and mixtures thereof.

Some non-acid monomers can also be included, usually in minor amounts,in preparing the hydrogel-forming absorbent polymers herein. Suchnon-acid monomers can include, for example, the water-soluble orwater-dispersible esters and amides of the acid-containing monomers, aswell as monomers that contain no carboxylic or sulfonic acid groups atall. Optional non-acid monomers can thus include monomers containing thefollowing types of functional groups: carboxylic acid or sulfonic acidesters and amides, hydroxyl groups, amino groups, nitrile groups,quaternary ammonium salt groups, ether groups, aryl groups (e.g., phenylgroups, such as those derived from styrene monomer). These non-acidmonomers are well-known materials and are described in greater detail,for example, in U.S. Pat. No. 4,076,663 (Masuda et al.), issued Feb. 28,1978, and in U.S. Pat. No. 4,062,817 (Westerman), issued Dec. 13, 1977,both of which are incorporated by reference.

Olefinically unsaturated carboxylic acid and carboxylic acid anhydridemonomers include the acrylic acids typified by acrylic acid itself,methacrylic acid, ethacrylic acid, α-chloroacrylic acid, α-cyanoacrylicacid, β-methylacrylic acid (crotonic acid), α-phenylacrylic acid,β-acryloxypropionic acid, sorbic acid, α-chlorosorbic acid, angelicacid, cinnamic acid, p-chlorocinnamic acid, β-sterylacrylic acid,itaconic acid, citraconic acid, mesaconic acid, glutaconic acid,aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleicacid anhydride.

Olefinically unsaturated sulfonic acid monomers include aliphatic oraromatic vinyl sulfonic acids such as vinylsulfonic acid, allyl sulfonicacid, vinyl toluene sulfonic acid and styrene sulfonic acid; acrylic andmethacrylic sulfonic acid such as sulfoethyl acrylate, sulfoethylmethacrylate, sulfopropyl acrylate, sulfopropyl methacrylate,2-hydroxy-3-methacryloxypropyl sulfonic acid and2-acrylamide-2-methylpropane sulfonic acid.

Preferred hydrogel-forming absorbent polymers for use in the presentinvention contain carboxy groups. These polymers include hydrolyzedstarch-acrylonitrile graft copolymers, partially neutralized hydrolyzedstarch-acrylonitrile graft copolymers, starch-acrylic acid graftcopolymers, partially neutralized starch-acrylic acid graft copolymers,saponified vinyl acetate-acrylic ester copolymers, hydrolyzedacrylonitrile or acrylamide copolymers, slightly network crosslinkedpolymers of any of the foregoing copolymers, partially neutralizedpolyacrylic acid, and slightly network crosslinked polymers of partiallyneutralized polyacrylic acid. These polymers can be used either solelyor in the form of a mixture of two or more different polymers. Examplesof these polymer materials are disclosed in U.S. Pat. No. 3,661,875,U.S. Pat. No. 4,076,663, U.S. Pat. No. 4,093,776, U.S. Pat. No.4,666,983, and U.S. Pat. No. 4,734,478.

Most preferred polymer materials for use in making the hydrogel-formingabsorbent polymers are slightly network crosslinked polymers ofpartially neutralized polyacrylic acids and starch derivatives thereof.Most preferably, the hydrogel-forming absorbent polymers comprise fromabout 50 to about 95%, preferably about 75%, neutralized, slightlynetwork crosslinked, polyacrylic acid (i.e., poly (sodiumacrylate/acrylic acid)). Network crosslinking renders the polymersubstantially water-insoluble and, in part, determines the absorptivecapacity and extractable polymer content characteristics of thehydrogel-forming absorbent polymers. Processes for network crosslinkingthese polymers and typical network crosslinking agents are described ingreater detail in U.S. Pat. No. 4,076,663.

Mixtures of polymers can also be used in the present invention. Forexample, mixtures of starch-acrylic acid graft copolymers and slightlynetwork crosslinked polymers of partially neutralized polyacrylic acidcan be used in the present invention. Mixtures or combinations of thedifferent relatively narrow size fractions of HFAPs can be useful in thepresent invention, e.g., small particles in one zone and large particlesin another. Mixtures or combinations of HFAPs of different morphologiesmay also be used, e.g., fibers in one zone and particulates in another.Small particles have a mean diameter less than about 100 μm and largeparticles have a mean diameter of greater than about 300 μm.

The “fast” HFAPs useful in the present invention will typically have arelatively high surface area to volume ratio. This can be achieved byvarying the size, shape and/or morphology over a wide range, e.g.,granules, pulverulents, interparticle aggregates, interparticlecrosslinked aggregates, and the like. These can be in the form offibers, sheets, films, foams, flakes and the like. The hydrogel-formingabsorbent polymers can also comprise mixtures with low levels of one ormore additives, such as for example powdered silica, surfactants, glue,binders, and the like, as referenced in U.S. Pat. No. 5,489,469. Thecomponents in this mixture can be physically and/or chemicallyassociated in a form such that the hydrogel-forming polymer componentand the non-hydrogel-forming polymer additive are not readily physicallyseparable. The HFAPs of the present invention may also be surfacetreated with a polyamine such as polyethylene imine or polyallyl amineso as to confer “stickiness” when wet as described in U.S. Pat. No.5,382,610 (Harada et al.) issued Jan. 17, 1995. This is one means forproviding wet core integrity.

One preferred means of creating a relatively high surface area to volumeratio in HFAPs is to form polymers having substantial internal porosity.Porosity can be generated by several means, including inclusion ofgas-generating additives (e.g., ammonium carbonate, toluene, alkanes,chlorofluorocarbons, and the like) in the polymer prior topolymerization. Examples are provided in U.S. Pat. No. 5,399,591, U.S.Pat. No. 5,154,713, U.S. Pat. No. 5,146,714, U.S. Pat. No. 5,403,870,U.S. Pat. No. 5,338,766, and U.S. Pat. No. 4,522,938, included herein byreference. A second preferred means of creating relatively high surfaceto volume is to form polymers in the shape of fibers, e.g., as isdescribed in U.S. Pat. No. 5,280,079 and U.S. Pat. No. 5,026,784included by reference herein. Indeed, fibers have a combination ofproperties useful herein, including speed of fluid imbibition and ofrelative ease of incorporation and containment in specific regionswithin the core structure. Yet another means is to form nonsphericalshapes which are complex and have significant surface area (while notbeing especially porous, as described in PCT World Patents 93/19,099 and92/16,565 (Stanley et al.) published Oct. 1, 1992. Yet another way is toselect very small particles, e.g., less than about 100 μm in diameter(though this often incurs undesirable properties associated with suchsmall sizes). Particle size is defined as the dimension determined bysieve size analysis. The mass median particle size of a given sample ofhydrogel-forming absorbent polymer particles is defined as the particlesize that divides the sample in half on a mass basis, i.e., one-half ofthe sample by weight will have a particle size less than the mass mediansize and one-half of the sample will have a particle size greater thanthe mass median size. A standard particle-size plotting method (whereinthe cumulative weight percent of the particle sample retained on orpassed through a given sieve size opening is plotted versus sieve sizeopening on probability paper) is typically used to determine mass medianparticle size when the 50% mass value does not correspond to the sizeopening of a U.S.A. Standard Testing Sieve. These methods fordetermining particle sizes of the hydrogel-forming absorbent polymerparticles are further described in U.S. Pat. No. 5,061,259 (Goldman et.al), issued Oct. 29, 1991, which is incorporated by reference. For HFAPswhich are used in the form of fibers, the key dimensions arecross-sectional diameter and fiber length.

For particles of hydrogel-forming absorbent polymers useful in thepresent invention, the particles will generally have a size of at least100 μm, and preferably will range in size from about 100 to about 2000μm, more preferably from about 200 to about 1000 μm. The mass medianparticle size will be at least 100 μm, and preferably will be from about250 to about 1000 μm, more preferably from about 300 μm to about 800microns, and even more preferably from about 350 to about 750 μm. ForHFAPs in the form of fibers, the cross-sectional diameters willgenerally range from about 5 μm to about 75 μm, preferably from about 10μm to about 35 μm. The fiber lengths can be indeterminate, thoughgenerally fiber lengths must exceed cross-sectional area by at leastabout a factor of 10, preferably at least about a factor of 100, to beconsidered a fiber and not simply a distended particle. Generally, fiberlengths will be between about 2 mm and about 20 mm.

Degradation in other hydrogel-forming absorbent polymer properties suchas rate (DGR), PHL, Performance Under Pressure (PUP) capacity, and levelof extractable polymer. Thus, for example, it can be useful to use asize cut having a mass median size in the range of from about 350 toabout 750 μm wherein only minimal mass fractions of the particulateshave sizes either greater than about 750 μm or less than about 350 μm.Alternatively, a broader size cut wherein the particles generally have asize in the range of from about 250 μm to about 1000 μm can be useful.

b. Physical Properties

The following describes in detail the ranges of each of the importantphysical properties necessary in the present invention. It will berecognized that while the present application describes absorbentmembers having one or more regions of at least about 50% by weight ofHFAPs where the HFAPs have certain gelling rates (DGR) and absorbencyunder pressure (PUP) values, it is possible to include HFAPs in the highconcentration region(s) that do not exhibit these DGR and PUP capacityvalues, while still practicing within the scope of the presentinvention. That is, by way of illustration only, it is possible toinclude in the high concentration region(s) a mixture of one or moreHFAPs wherein at least one HFAP does not exhibit a DGR value of at aboutleast 0.18 g/g/sec and/or a PUP capacity of at least about 25 g/g, alongwith one or more different HFAPs that do exhibit these properties. Aspecific example, by way of illustration only, comprises use of a regioncomprising 50% by total weight HFAP wherein 20% of the HFAP (by totalHFAP weight) is outside the present invention and 80% (by total HFAPweight) of the HFAP is within the present invention. In thisillustration, even though only about 40% of the region(s) of theabsorbent member comprises HFAPs meeting the described DGR and PUPvalues, the member would be within the scope of the present invention solong as the DGR and PUP values (and for particles, a mass medianparticle size) for a mixture within at least one region are within thescope of the present invention as described below. In this regard, itwill be preferred that the high concentration region(s) of the absorbentmember will comprise at least about 30% HFAPs, by total weight of theHFAPs in a region, having the DGR and PUP values described below. Morepreferably, the absorbent member will comprise at least about 35% HFAPs,still more preferably at least about 40% HFAPs, by total weight of theHFAPs in a region, having the DGR and PUP values described below. Insuch cases, the balance of HFAP used may have properties outside thepresent invention and will be used in an amount necessary to bring thetotal HFAP concentration in the region up to at least about 50%. Suchmixtures of HFAPs of different types may be used homogeneouslythroughout the core or separately within specific regions, such as onetype in the loading zone and another type in the storage zone.

(1) Rate of Gelling

A characteristic of the hydrogel-forming absorbent polymers useful inthe present invention is the rate of gelling. The rate of gelling isexpressed herein in terms of the Dynamic Gelling Rate (DGR) using themethod described hereinafter. The HFAPs of the present invention haveDGR values of at least about 0.18 g/g/sec, preferably at least about0.25 g/g/sec, more preferably at least about 0.28 g/g/sec and mostpreferably at least about 0.32 g/g/sec.

(2) Performance under Pressure (PUP)

Another characteristic of the hydrogel-forming absorbent polymers usefulin the present invention is their demand absorbency capacity under ahigh confining pressure. This demand-absorbency capacity is defined interms of the Polymer's Performance under Pressure (PUP) capacity. ThePUP capacity of hydrogel-forming absorbent polymers useful in thepresent invention is generally at least about 25 g/g, preferably atleast about 29 g/g, and more preferably at least about 32 g/g.Typically, these PUP capacity values are in the range of from about 25to about 45 g/g, more typically from about 29 to about 40 g/g, and mosttypically from about 32 to about 38 g/g. A method for determining thePUP capacity value of these hydrogel-forming absorbent polymers isprovided in U.S. Pat. No. 5,599,335 (supra).

(3) Size

Still another characteristic of the hydrogel-forming absorbent polymersuseful in the present invention, when in the form of particles, is theirparticle size. Size is defined in terms of the weight fractions that areretained or passed by sieves with different spacings, as definedhereinabove. Very small particles, less than about 100 μm, are notpreferred due to their propensity to gel block, their lower gel volumeswhen surface crosslinked, and issues with hygiene in manufacturingenvironments. While larger sized particulates tend also to have slowerrates of absorption, the HFAPs preferred in the present invention have auseful combination of rate and larger particle size, at least about 100μm and preferably at least about 300 μm. Preferred ranges for massmedian particle are discussed in detail, supra.

(4) Porosity of Hydrogel Zone or Layer

A characteristic that can be important for the hydrogel-formingabsorbent polymers useful in the present invention is the openness orporosity of the hydrogel (PHL) zone or layer formed when the polymer isswollen in body fluids under a confining pressure. PHL measures theability of the formed hydrogel zone or layer to remain open so as to beable to acquire and distribute body fluids under usage pressures.Porosity of the hydrogel zone or layer is also can affect the demandwettability or gravimetric absorbency capacity (i.e., PUP capacity) andwicking properties as described in U.S. Pat. No. 5,562,646 (supra). Theporosity of the hydrogel zone or layer is also important because of itsimpact on permeability (i.e., SFC values) of the hydrogel zone/layer.Higher porosity is an important contributor to higher permeability,particularly for the very fast HFAPs of the present invention used atrelatively high concentrations in the loading zone of the absorbentcore.

Hydrogel-forming absorbent polymers useful in the present invention havePHL values of at least about 0.15, preferably at least about 0.18, morepreferably at least about 0.18 and most preferably at least about 0.25.Typically, these PHL values are in the range of from about 0.15 to about0.40, and more typically from about 0.18 to 0.25. A method fordetermining the PHL value of these hydrogel-forming absorbent polymersis provided in U.S. Pat. No. 5,562,646 (supra).

(5) Saline Flow Conductivity (SFC)

Another characteristic that can be important for the hydrogel-formingabsorbent polymers useful in the present invention is their permeabilityor flow conductivity when swollen with body fluids so as to form ahydrogel zone or layer. This permeability or flow conductivity isdefined herein in terms of the Saline Flow Conductivity (SFC) value ofthe hydrogel-forming absorbent polymer as described in U.S. Pat. No.5,599,335 (supra). The SFC value of the hydrogel-forming absorbentpolymers useful in the present invention is at least about 30×10⁻⁷cm³sec/g, preferably at least about 50×10⁻⁷ cm³sec/g, and mostpreferably at least about 75×10⁻⁷ cm³sec/g. Typically, these SFC valuesare in the range of from about 30 to about 1000×10⁻⁷ cm³sec/g. A methodfor determining the SFC value of these hydrogel-forming absorbentpolymers is provided in U.S. Pat. No. 5,599,335 (supra).

(6) Extractable Polymer

Another characteristic that can be important for hydrogel-formingabsorbent polymers useful in the present invention is the level ofextractable polymer material present therein. See U.S. Pat. No.4,654,039 (Brandt et al.), issued Mar. 31, 1987 (reissued Apr. 19, 1988as Re. 32,649). Extracted polymer material can alter both the chemicalcharacteristics (e.g., osmolarity) and physical characteristics (e.g.,viscosity) of the body fluid to such an extent that the fluid is moreslowly absorbed and more poorly held by the hydrogel. Also, the PUPcapacity can actually decline over time if extractables levels are toohigh. This is particularly problematic in the high concentrationabsorbent cores of the present invention.

The preferred levels of extractable polymer for hydrogel-formingabsorbent polymers useful in the present invention are about 15% orless, more preferably about 10% or less, and most preferably about 7% orless of the total polymer. Methods for determining the levels ofextractable polymer in these hydrogel-forming absorbent polymersinvention are provided in U.S. Pat. No. 5,599,335 (supra).

(7) Gel Volume

Yet another characteristic that can be important for hydrogel-formingabsorbent polymers useful in the present invention is gel volume. Asused herein, the “gel volume” of a hydrogel-forming absorbent polymer isdefined as its free-swell absorbent capacity when swollen in an excessof Jayco synthetic urine, unless the solution is otherwise specified. Itprovides a measure of the maximum absorbent capacity of the polymerunder conditions of use where the pressures on the polymer arerelatively low. Methods for determining the gel volumes of thesehydrogel-forming polymers are provided in U.S. Pat. No. 5,599,335(supra). The preferred gel volumes of the hydrogel-forming absorbentpolymers of the present invention are at least about 25 g/g, morepreferably at least about 35 g/g, and most preferably at least about 45g/g. Typically, these gel volumes are in the range of from about 25 toabout 100 g/g, more typically from about 30 to about 80 g/g, and mosttypically from about 35 to about 70 g/g.

(8) Gel Strength

Still another characteristic that can be important for hydrogel-formingabsorbent polymers useful in the present invention is gel strength. Asused herein, “gel strength” relates to the tendency of the hydrogelformed from the absorbent polymer to deform or “flow” under usagestresses. Gel strength needs to be such that the hydrogel does notdeform and fill to an unacceptable degree the void spaces between thehydrogel and the other components in the absorbent member. In general,increasing gel strength will result in an increase in the permeabilityand porosity of a hydrogel zone or layer formed from thehydrogel-forming absorbent polymer. A method for determining the gelstrength of the hydrogel-forming absorbent polymers of the presentinvention is provided in U.S. Pat. No. 5,599,335 (supra). It ispreferred that the gel strength of the hydrogel-forming absorbentpolymers of the present invention be at least about 10,000 dynes/cm²,more preferably at least about 20,000 dynes/cm², and most preferably atleast about 40,000 dynes/cm².

c. Methods for Making

The basic hydrogel-forming absorbent polymer can be formed in anyconventional manner. Typical and preferred processes for producing thesepolymers are described in U.S. Reissue Pat. No. 32,649 (Brandt et al.),issued Apr. 19, 1988, U.S. Pat. No. 4,666,983 (Tsubakimoto et al.),issued May 19, 1987, and U.S. Pat. No. 4,625,001 (Tsubakimoto et al.),issued Nov. 25, 1986, all of which are incorporated by reference. Otherpreferred methods and variations are described in more detail in U.S.Pat. No. 5,599,335 (supra).

d. Surface Crosslinking

Surface crosslinked hydrogel-forming absorbent polymers have a higherlevel of crosslinking in the vicinity of the surface than in theinterior. As used herein, “surface” describes the outer-facingboundaries of the particle, fiber, etc. For porous hydrogel-formingabsorbent polymers (e.g., porous particles, etc.), exposed internalboundaries can also be included. By a higher level of crosslinking atthe surface, it is meant that the level of functional crosslinks for thehydrogel-forming absorbent polymer in the vicinity of the surface isgenerally higher than the level of functional crosslinks for the polymerin the interior.

The gradation in crosslinking from surface to interior can vary, both indepth and profile. Thus, for example, the depth of surface crosslinkingcan be shallow, with a relatively sharp transition to a lower level ofcrosslinking. Alternatively, for example, the depth of surfacecrosslinking can be a significant fraction of the dimensions of thehydrogel-forming absorbent polymer, with a broader transition.

Depending on size, shape, porosity as well as functional considerations,the degree and gradient of surface crosslinking can vary within a givenhydrogel-forming absorbent polymer. For particulate hydrogel-formingabsorbent polymers, surface crosslinking can vary with particle size,porosity, etc. Depending on variations in surface:volume ratio withinthe hydrogel-forming absorbent polymer (e.g., between small and largeparticles), it is not unusual for the overall level of crosslinking tovary within the material (e.g., be greater for smaller particles).

Surface crosslinking is generally accomplished after the finalboundaries of the hydrogel-forming absorbent polymer are essentiallyestablished (e.g., by grinding, extruding, foaming, etc.) However, it isalso possible to effect surface crosslinking concurrent with thecreation of final boundaries. Furthermore, some additional changes inboundaries can occur even after surface crosslinks are introduced.Surface crosslinking is of particular import with the faster HFAPs ofthe present invention. To the extent that speed is achieved byincreasing the surface area:volume ratio of the HFAP, this also exposesmore surface area for surface crosslinking with potential for associatedreduction in gel volume as a result. Thus, it is particularly preferablethat the surface crosslinking technique be one wherein the depth of thesurface is relatively thin. This is achieved more typically by use ofmore reactive surface crosslinking agents, described in U.S. Pat. No.5,599,335 (supra).

Suitable general methods for carrying out surface crosslinking ofhydrogel-forming absorbent polymers according to the present inventionare disclosed in U.S. Pat. No. 5,597,873 (Chambers et al.) issued Jan.28, 1997, in U.S. Pat. No. 4,541,871 (Obayashi), issued Sep. 17, 1985,U.S. Pat. No. 5,447,727 (Graham) issued Sep. 5, 1995, U.S. Pat. No.5,385,983 (Graham) issued Jan. 31, 1995, U.S. Pat. No. 5,475,062(Ishizaki et al.) issued Dec. 12, 1995, published PCT application WO92/16565 (Stanley), published Oct. 1, 1992, published PCT application WO90/08789 (Tai), published Aug. 9, 1990; published PCT application WO93/05080 (Stanley), published Mar. 18, 1993; U.S. Pat. No. 4,824,901(Alexander), issued Apr. 25, 1989; U.S. Pat. No. 4,789,861 (Johnson),issued Jan. 17, 1989; U.S. Pat. No. 4,587,308 (Makita), issued May 6,1986; U.S. Pat. No. 4,734,478 (Tsubakimoto), issued Mar. 29, 1988; U.S.Pat. No. 5,164,459 (Kimura et. al.), issued Nov. 17, 1992; publishedGerman patent application 4,020,780 (Dahmen), published Aug. 29, 1991;and published European patent application 509,708 (Gartner), publishedOct. 21, 1992; all of which are incorporated by reference.

The hydrogel-forming absorbent polymer particles used in the presentinvention are typically substantially dry. The term “substantially dry”is used herein to mean that the particles have a fluid content,typically water or other solution content, less than about 50%,preferably less than about 20%, more preferably less than about 10%, byweight of the particles when employed to make absorbent cores or testmeasurements.

e. Specific Examples

The following provides some specific examples of hydrogel-formingabsorbent polymers suitable for use in the present invention:

EXAMPLE 1 Properties of Hydrogel-Forming Absorbent Polymers FromCommercial Sources

The properties of certain particulate partially-neutralized sodiumpolyacrylate hydrogel-forming polymers obtained from commercial sourcesuseful in the present invention are shown in Table 1:

TABLE 1 Gel Volume^(a) DGR PUP SFC in 0.9% g/g/sec g/g ×10⁻⁷ SampleSaline (k × 0.7 cm³sec/ Number HFAP Type Mfg. (g/g) GV) psi g 1Fibersorb Arco¹ 57.0 2.13 6.5 0.1 2 Fiberdri Camelot¹ 37.0 1.21 8.0 11613 Oasis TAL³ 33.7 0.97 10.2 10 4 VP 101A NSKK⁴ 29.3 0.55 15.2 5 M-8547NSKK⁴ 33.7 0.42 27.0 4 6 3936-196 Nalco⁵ 27.0 0.32 30.7 32 7 M-8161NSKK⁴ 36.6 0.30 33.8 10 8 HC Z-5 H-C⁶ 41.3 0.21 34.1 36 9 HC Z-4 H-C⁶39.9 0.18 35.3 20 10 N1180 Nalco⁵ 33.9 0.17 9.1 0.1 11 L-761f NSKK⁴ 34.00.13 25.4 5 12 ASAP 2300 Chemdal² 38.1 0.099 35.2 66 ¹ARCO = AtlanticRichfield, Co., which sold its HFAP fiber operations to Camelot, Inc.,Charlotte, NC and Calgary, Alberta. ²Chemdal Corporation of Palatine,Illinois. ³Technical Absorbents Limited, Grimsby, Great Britain. ⁴NipponShokubai of Hmeji, Japan. ⁵Nalco Chemical Company of Naperville,Illinois. ⁶Hoechst-Celanese of Portsmouth, VA. ⁷Stockhausen, ChemischeFabrik Stockhausen GmbH of Krefeld, Germany. ^(a)Gel Volumes listed inTable 1 are measured according to the method described in the TestMethods section, except 0.9% saline is used as the test solution.

Sample numbers 5 through 9 illustrate HFAPs of the present invention.Sample numbers 1-4 have fast rates but insufficient PUP values. Samples10-12 have rates that are slower than the HFAPs useful herein.

EXAMPLE 2 Absorbent Core of the Present Invention

An absorbent core is created by air laying a core comprising 15% fluffpulp fibers, 25% curly fibers, and 60% M8161 from Example 1. This coreabsorbs fluid quickly and efficiently without gel blocking.

2. Fibrous Materials

The absorbent members of the present invention can comprise fibrousmaterials to form fibrous web or fibrous matrices. Fibers useful in thepresent invention include those that are naturally occurring fibers(modified or unmodified), as well as synthetically made fibers. Adetailed compendium of fibers types and their uses in absorbent cores isin U.S. Pat. No. 5,599,335 (supra).

3. Thermoplastic Materials

In the case of thermally bonded absorbent members according to thepresent invention, the member can comprise thermoplastic material inaddition to the fibers. Upon melting, at least a portion of thisthermoplastic material migrates to the intersections of the fibers,typically due to interfiber capillary gradients. These intersectionsbecome bond sites for the thermoplastic material. When cooled, thethermoplastic materials at these intersections solidify to form the bondsites that hold the matrix or web of fibers together in each of therespective layers. The varied employment of thermoplastic materials inabsorbent cores is detailed in U.S. Pat. Nos. 5,599,335 and 5,607,414incorporated herein by reference.

4. Other Components and Materials

Absorbent members according to the present invention can include otheroptional components that can be present in absorbent webs. For example,a reinforcing scrim can be positioned within the absorbent member, orbetween the respective absorbent members, of the absorbent core. Suchreinforcing scrims should be of such configuration as to not forminterfacial barriers to fluid transfer, especially if positioned betweenthe respective absorbent members of the absorbent core. Also, whenhydrogel-forming absorbent polymers are present in one or more absorbentmembers of the absorbent core, the respective absorbent member, or theentire absorbent core, can be enveloped within a fluid pervious sheet,such as a tissue paper sheet, to obviate user concern regarding looseparticulate absorbent polymer. Other optional components that can beincluded are materials to control odor, adhesives, contain fecal matter,etc.

Absorbent members according to the present invention can also includefoam-based absorbents. Suitable foam absorbents include those describedin U.S. Pat. No. 5,260,345 (DesMarais et al.), issued Nov. 9, 1993, U.S.Pat. No. 5,147,345 (Young et al.), issued Sep. 15, 1992, U.S. Pat. No.5,387,207 (Dyer et al.) issued Feb. 7, 1995, all of which areincorporated by reference.

C. Absorbent Members Containing Hydrogel-Forming Absorbent Polymers

1. Concentration, Basis Weight and Fluid Handling Properties

At least one of the absorbent members according to the present inventionwill comprise the previously described hydrogel-forming absorbentpolymers, with or without other optional components such as fibers,thermoplastic material, etc. These absorbent members comprising theseabsorbent polymers can function as fluid storage members in theabsorbent core. The principle function of such fluid storage members isto absorb the discharged body fluid either directly or from otherabsorbent members (e.g., fluid acquisition/distribution members), andthen retain such fluid, even when subjected to pressures normallyencountered as a result of the wearer's movements. It should beunderstood, however, that such polymer-containing absorbent members canserve functions other than fluid storage.

An important aspect of these absorbent members according to the presentinvention is that they contain one or more regions having a highconcentration of these hydrogel-forming absorbent polymers. In order toprovide relatively thin absorbent articles capable of absorbing andretaining large quantities of body fluids, it is desirable to increasethe level of these hydrogel-forming absorbent polymers and to reduce thelevel of other components, in particular fibrous components.

In order to utilize these hydrogel-forming absorbent polymers atrelatively high concentrations for fluid storage, these polymers shouldhave a relatively high gelling rate (i.e., DGR value) as well as arelatively high demand absorbency capacity under a relatively highconfining pressure (i.e., PUP capacity value) and preferably arelatively high permeability under pressure (i.e., SFC value) andporosity (PHL value). This is so that the polymer in the presence ofbody fluids acquires these discharged body fluids rapidly.

An important aspect of the present invention is that HFAPs with highrates used in the storage zone of the core also have very high SFCvalues. This is believed to be because very rapid gellation of the HFAPcan tend to diminish the interstitial volume available which is criticalfor rapid imbibition of gushes. For example, baby diapers can experiencegushes of 75 mL urine in 15 seconds (15 mL/second for 5 seconds). Atypical diaper core might contain about 10 g of HFAP. If all 10 g wereavailable for gelling of this gush (which is not generally the case),the rate of acquisition would have to be 15 mL urine/10 g HFAP/second,or about 1.5 g/g/sec. The high relative permeability (SFC value)substantially reduces the propensity for gel blocking in such instances.

The concentration of the hydrogel-forming absorbent polymers in a givenregion of an absorbent member according to the present invention can bein the range of from about 50 to 100%, preferably from about 60 to 100%,more preferably from about 70 to 100%, still more preferably from about80 to 100%, and most preferably from about 90% to 100%, measured asdefined in U.S. Pat. No. 5,599,335, which is incorporated herein byreference. The HFAPs useful in the present invention may be combinedwith HFAPs with properties outside those specified in the currentinvention. In cases wherein HFAPs of two different kinds are combined inthe absorbent core, combined properties of the HFAP in the amounts andratios specified are relevant. Another important aspect is the basisweight of the hydrogel-forming absorbent polymer in a given region ofthe absorbent member, which is also measured as defined in U.S. Pat. No.5,607,414. The basis weight of a hydrogel-forming absorbent polymer in agiven region of an absorbent member according to the present inventionis at least about 10 gsm, preferably at least about 20 gsm, morepreferably at least about 50 gsm, and most preferably at least about 100gsm. Typically, these basis weight values are in the range of from about10 to about 1000 gsm, more typically from about 50 to about 800 gsm, andmost typically from about 100 to about 600 gsm.

2. Wet Integrity of Absorbent Member and/or Absorbent Core

During initial fluid acquisition, absorbent core utilization occurs inthe immediate vicinity of the gush. There is a need to gain as muchlateral (i.e., X-Y dimension) fluid movement as possible in the storageregions of the core, particularly as the absorbent cores become thinnerand thinner.

The hydrogel-containing regions preferably retain a certain amount ofphysical continuity for adequate fluid movement to take place throughcontiguous interstitial voids and capillaries. Realization of thebenefits of the hydrogel-forming absorbent polymers is facilitated byabsorbent members and absorbent cores that provide good wet integrity.By “good wet integrity” is meant that the region or regions in theabsorbent member having the high concentration of hydrogel-formingabsorbent polymer have sufficient integrity in a dry, partially wet,and/or wetted state such that the physical continuity (and thus thecapability of acquiring and transporting fluid through contiguousinterstitial voids/capillaries) of the gel-continuous fluidtransportation zone or layer formed upon swelling of thehydrogel-forming absorbent polymer in the presence of body fluids is notsubstantially disrupted or altered, even when subjected to normal useconditions. Such use conditions and various measures that can be takento enhance wet integrity are described in more detail in absorbent coresis in U.S. Pat. No. 5,599,335 (supra).

D. Absorbent Cores

Absorbent members according to the present invention comprising highconcentrations of hydrogel-forming absorbent polymers are useful aloneor in combination with other absorbent members in a variety of absorbentcores. A wide variety of absorbent cores and their components aredescribed in U.S. Pat. No. 5,599,335 (supra).

E. Absorbent Articles

Because of the unique absorbent properties of the absorbent cores of thepresent invention, they are especially suitable for use in absorbentarticles, especially disposable absorbent articles. Preferredembodiments of a disposable absorbent article according to the presentinvention are diaper and catamenial pads. It should be understood,however, that the present invention is also applicable to otherabsorbent articles such as incontinent briefs, incontinent pads,training pants, diaper inserts, sanitary napkins, facial tissues, papertowels, bandages, cable wrappings, water-proofing layers, and the like.

A general description of the variety of absorbent articles which may beconstructed is detailed in U.S. Pat. No. 5,599,335 (supra). Thesegenerally comprise a fluid impervious backsheet, a topsheet, anabsorbent core, and various attachments (e.g., tapes, adhesives,elastics, etc.). The absorbent cores containing HFAPs of the currentinvention can be useful in any of the designs described therein.

F. Test Methods

1. Dynamic Gelling Rate (DGR)

This test determines the Dynamic Gelling Rate (DGR) of thehydrogel-forming absorbent polymer stirred in excess 0.03% bluedextran/0.9% sodium chloride solution (saline). This solution isprepared by dissolving 9.0 g sodium chloride and 0.300 g blue dextran(obtained from Sigma Chemical Co. Catalog Number D-5751) in 1 Ldistilled water. As shown in FIG. 1. the DGR testing device, depictedgenerally as 10, comprises a peristaltic pump 11, a self-cleaningfiltering device 12 comprising a motor 12 a, a hemi-spherical mixingchamber 13, an overhead stirring system 14 consisting of a motor and astirring rod having a 2-blade propeller, a sampling assembly showngenerally as 15, a colorimeter 16, and a data collecting device 17. DGRtesting device 10 further comprises tubing 18 which connects filteringdevice 12, peristaltic pump 11 and sampling assembly 15; and tubing 19which connects sampling assembly 15 and filtering device 12.

The self-cleaning filtering device 12 is depicted in detail in FIG. 2a.The filtering device 12 comprises a rotating vane assembly 21, whichturns in a direction 21 a, a 2 in. diameter cylindrical housing 22 whichis sealed into the side of the hemi-spherical mixing chamber 13, a meshscreen 23 attached to rotating vane assembly 21, an inlet port 24 andoutlet port 25. Ports 24 and 25 enter cylindrical housing 22 andterminate just behind screen 23. As shown in FIG. 2b, the inlet port 24immediately behind the screen 23 is a 0.375 in. diameter openingrecessed within a 0.25 in. deep/0.5 in. diameter opening. The outletport 25 is a 0.375 in. diameter opening within a rounded quarter moonopening which is 0.25 in. deep, 0.44 in. wide and comprises nearly theentire lower half of the cylindrical housing 22.

The mixing chamber 13 is shown in detail in FIG. 3, and comprisesmachined Plexiglas® curved to form a symmetrical ( )-shaped vessel toenhance mixing. [Applicants specifically modified a cylindrical vessel(10 cm internal diameter; 7 cm deep), shown in FIG. 3 as 29, by adding acurved Plexiglas® wall 28 such that the symmetrical vessel 13 formed is9.0 cm in the larger internal dimension, 5.3 cm in the smaller internaldimension, and 7 cm in depth. Stirring is effected with a glasspaddle-style stirrer (4 cm diameter and 1.5 cm blade thickness canted ata 45° angle) from an overhead laboratory stirrer motor, the system beingdepicted in FIG. 1 as 14.

Various aspects of sample assembly 15 depicted in FIG. 1 are shown inmore detail in FIGS. 4a, 4 b and 4 c. From these Figures, it is seenthat the sample assembly comprises a threaded adapter (31 in FIG. 4a), afiberoptic probe (51 in FIG. 4c) and a fiberoptic probe holder (41 inFIG. 4b). Adapter 31 functions to position the fiberoptic probe suchthat it can measure the absorbency characteristics of the fluid passingfrom inlet glass 32 to glass outlet 33 of adapter 31. In particular, thefiberoptic probe holder 41 shown in FIG. 4b is constructed from Teflon®and is threaded such that it can be screwed into threaded adapter 31.When probe 51 is inserted in holder 41 through hole 42 and holder 41 istightened into adapter 31, probe 51 is securely held in place in thepath of the fluid flowing through threaded adapter 31. Leads 52 of probe51 send absorbency data to colorimeter 16. Adapter 31 is a custom madeglass cell having a 2 mm i.d. glass inlet 32 and a 2 mm i.d. glassoutlet 33, and also comprises a rubber O-ring 34 to ensure water-prooffit. Adapter 31 also comprises a threaded receiving body indicatedgenerally as 35 for securely receiving probe holder 41.

With reference to all of the figures, the DGR method proceeds generallyas follows. Pumping of test fluid from mixing chamber 13 to sampleassembly 15 is effected via pump 11 (e.g., an easyload Masterflex model7518-10 peristaltic pump unit) with tubing 18 (e.g., Norton Tygon®flexible tubing (⅛ in. i.d., ¼ in. o.d., {fraction (1/16)} in. wall andformula R-3603 from VWR Scientific #63010-020)). Tubing 18 is replacedafter 90 minutes of use or each day, whichever comes first. The samplingis through self-cleaning filtering device 12 comprising a screen 23(e.g., a No. 400 mesh screen) attached to the rotating vane. Theself-cleaning filtration device 12 is rotating at 45 rpm. To prevent theHFAP from blocking the screen, a much smaller sample return (or inlet)port 24 relative to sampling (or outlet) port 25 behind the attachedscreen is used to remove any gel with each revolution. The difference inpressure maintains a clean screen. The HFAP-containing solution is mixedvia stirrer 14 (e.g., a T-line laboratory stirrer (model 134-2)), at astirring rate of 640 rpm. Pump rates for peristaltic pump 11 are set toapproximately 6 (approximately 250 mL/min with described tubing). Thisincurs a 5-7 second delay between the mixing vessel and thespectrophotometer. Although this flow can be easily increased,experience has shown that cavitation is much more likely at higherflows. Two centimeters of tubing 19 connect the outlet port 28 of thefiltering device 12 to a custom made glass cell 31 (shown in FIGS. 4a-c)into which the fiber-optic probe 51 of the calorimeter fits exactly.This length of tubing is used to secure the connection and doesn'teffect the distance. The actual distance from the exit port of thefiltering device 12 to the probe 51 remains at 4 cm. The tubing 18 whichpasses from the sampling device 15 through the peristaltic pump 11 andto the sample return port 24 of the mixing chamber is 41 cm in length.

Optical absorbency readings are measured using a Brinkman ColorimeterModel PC-900 with a 620 nm bandpass filter or an equivalent colorimeter.The calorimeter 16 uses a fiberoptic probe 51 with a 2 cm (total)pathlength. Air bubbles are eliminated from the sample assembly 15before data are collected to reduce noise.

The solution is unthermostated. The temperature during the course ofthese experiments should be 22°±2° C. The Colorimeter sends data every1.26 seconds. Data are collected for at least 90 seconds via an RS-232interface using a Toshiba 3100e computer using an appropriateinterfacing software program (Symphony 2.2 with appropriatecommunications settings is used.) (For HFAPs outside the presentinvention, the rate of gelling may be so slow that 90 seconds isinsufficient. At least about 30% of the full gelling curve should betaken in such cases, up to about 5 minutes.) The data are then line fitby regression analysis to provide the DGR. The following is the stepwiseprocedure.

Step 1. Preparing the Apparatus. To the mixing chamber 13 is added >200mL of water. Then, the return (upper) tubing 18 is disconnected. Using alarge pipette bulb, water is drawn into the tubing 18 to displace thetrapped air behind the self-cleaning filtering device 12. (Displacementof nearly all trapped air is critical to this test. Very small airbubbles in the path length result in high and/or erratic absorbencyreadings.) Using the pipette bulb and approximately 7 mm i.d. Tygon®tubing, water is siphoned from the mixing chamber 13. The remainingwater is blotted up (e.g., with Kimwipes). Two hundred grams of the0.03% blue dextran in saline solution is weighed into a beaker andtransferred to the mixing chamber 13. The volume of fluid held in tubing18 and 19 is approximately 3.4 mL. This volume has minimal effect on theabsorbency value of the blue dextran solution. If air is trapped behindthe screen 23 of filtering device 12, the upper tubing 18 must beremoved and the above process repeated. The components of the apparatusare activated (stirrer, peristaltic pump 11 and the self-cleaningfiltering device 12) to verify that air isn't being pumped through thePC 900 probe light path.

Step 2. Begin Experiment. The computer with the appropriate softwareremains on at all times. The components including the colorimeter aredeactivated. HFAP is weighed to approximately 1.0 gm (record weight tothe nearest tenth of a milligram) onto weighing paper. Components areactivated. The colorimeter is last to be activated. As the colorimeter16 is turned on, it cycles through its start-up procedure. The datacollection device 17 begins receiving data (optical absorbency (0.000))in the light path every 1.26 seconds. The colorimeter zeroes the opticalabsorbency (typically 0.000 to 0.005) even though the solution containsblue dextran. The HFAP is added simultaneously to the stirring fluid inthe mixing chamber 13 with the fifth reading (t=0). (Preceding nullreadings are deleted in the analysis.) After the desired period of datacollection, the colorimeter 16 is turned off along with theself-cleaning filtering device 12/12 a and the peristaltic pump 11. Thefinal component turned off is the stirrer 14. The saline solution andthe hydrated HFAP is siphoned from the mixing chamber 13 into a beaker.The chamber is replenished with approximately 200 mL of deionized water.The stirrer is reactivated and water siphoned from the chamber quickly.This is repeated a third time. A paper towel is used to dry the chamberand remove any remaining HFAP.

Step 3. Subsequent Experiments. Subsequent experiments are initiated byplacing a fresh supply of blue dextran/saline solution (200.0 g) intothe mixing chamber 13, removing any entrapped air from the system asdescribed above and repeating the process beginning with all componentsbeing turned on to verify that all air has been removed. Theself-cleaning filtration device 12 is rotating at 45 rpm.

Step 4: Data Analysis. Conversion from optical absorbence values to gelvolume is effected using the following equation:

GV (g/g, t)=[1-(A _(o)/(A _(t) +A _(o corr).)]×[mL BD soln./g HFAP (dryweight)]

where A_(o) is the optical absorbency reading of the stock bluedextran/saline solution. This reading is obtained separately and istypically around 0.483 for a 0.03% blue dextran (BD) solution. This canvary from lot to lot of blue dextran. A_(t) refers to the opticalabsorbency reading at a given elapsed time t as recorded by thesoftware. A_(o corr.) is the optical absorbency reading of the stockblue dextran/saline solution corrected for the t=0 absorbency reading.As mentioned, this may vary (e.g. 0.000 to 0.005). This correctionprovides for the absolute change in absorbency. For example, A_(o corr.)is 0.481 if the t=0 reading is 0.002. A corrected spreadsheet withelapsed time in one column and gel volume (g/g) in the adjacent columnis prepared. A third column (Y) is generated using the equation:

Y=In (GV _(o)/(GV _(o) −GV _(t)))

where GV_(o) is the final equilibrium gel volume and GV_(t) is the gelvolume at the specified elapsed time for that row. GV_(o) may bedetermined from the plateau value at the end of the DGR experiment or ina separate gel volume method using blue dextran in saline as describedsupra. The Y data are plotted against elapsed time and the slope of theline (determined by linear regression) gives the rate constant for thereaction, k. The value k is multiplied by GV_(o) to give the initialrate, or DGR, in units of g/g/sec. The regression coefficient, r²,should be at least 0.95. Otherwise, the value for GV_(o) should berechecked to ensure the blue dextran has not interacted with the HFAP.

Step 5: Alternate Methods. The size-exclusion polymer used for thismethod should not be appreciably absorbed by the HFAP or the resultanthydrogel. For anionic HFAPs, blue dextran is particularly suitable foruse as a size-exclusion polymer since it is not appreciably absorbed.For HFAPs that absorb blue dextran (e.g., cationic HFAPs), it may benecessary to use an alternative size-exclusion polymer (e.g., ahigh-molecular weight Dextran with a suitable covalently-bonded cationicchromophore) or an alternative detection method (e.g., refractive index,scintillation) for determining relative solution concentrations of thesize-exclusion polymer. For HFAPs that appreciably absorb blue dextran,these alternative size-exclusion polymers and/or methods of detectionmay also need to be used for the measurement of gel volume and PHL.

What is claimed is:
 1. An absorbent member for the containment ofaqueous body fluids, which comprises at least one region comprisinghydrogel-forming absorbent polymer in a concentration of from 50 to 100%by weight, said hydrogel-forming absorbent polymer having: (a) aPerformance under Pressure (PUP) capacity value of at least 25 g/g undera confining pressure of 0.7 psi (5 kPa); (b) a Dynamic Gelling Rate(DGR) value of at least 0.18 g/g/sec; and (c) when the hydrogel-formingabsorbent polymer is in the form of particles, a mass median particlesize of at least 100 μm.
 2. The absorbent member of claim 1 wherein saidhydrogel-forming absorbent polymer has a DGR value of at least about0.25 g/g/sec.
 3. The absorbent member of claim 2 wherein saidhydrogel-forming absorbent polymer has a DGR value of at least about0.28 g/g/sec.
 4. An absorbent core for acquiring, distributing andstoring body fluids, which comprises the absorbent member of claim
 3. 5.The absorbent member of claim 3 wherein said hydrogel-forming absorbentpolymer has a DGR value of at least about 0.32 g/g/sec.
 6. The absorbentmember of claim 1 wherein said hydrogel-forming absorbent polymer has aPUP capacity value of at least about 29 g/g under a confining pressureof 0.7 psi (5 kPa).
 7. An absorbent core for acquiring, distributing andstoring body fluids, which comprises the absorbent member of claim
 6. 8.The absorbent member of claim 6 wherein said hydrogel-forming absorbentpolymer has a PUP capacity value of at least about 32 g/g under aconfining pressure of 0.7 psi (5 kPa).
 9. The absorbent member of claim8 wherein said hydrogel-forming absorbent polymer is in the form ofparticles, and wherein the particles have a mass median particle size offrom about 250 to about 1000 μm.
 10. An absorbent core for acquiring,distributing and storing body fluids, which comprises the absorbentmember of claim
 9. 11. The absorbent member of claim 1 wherein thehydrogel-forming absorbent polymer is in the form of unagglomeratedparticles.
 12. An absorbent core for acquiring, distributing and storingbody fluids, which comprises the absorbent member of claim
 11. 13. Theabsorbent member of claim 1 wherein said hydrogel-forming absorbentpolymer has a saline flow conductivity value of at least about 30×10⁻⁷cm³sec/g.
 14. The absorbent member of claim 1 wherein saidhydrogel-forming absorbent polymer has a Porosity of the Hydrogel Layer(PHL) of at least about 0.15.
 15. The absorbent member of claim 1wherein said hydrogel-forming absorbent polymer has less than about 15%extractable polymer material.
 16. The absorbent member of claim 1wherein said hydrogel-forming absorbent polymer has a gel volume of atleast about 35 g/g.
 17. The absorbent member of claim 1 wherein saidhydrogel-forming absorbent polymer has a gel strength of at least about10,000 dynes/cm².
 18. The absorbent member of claim 1 wherein saidhydrogel-forming absorbent polymer is in the form of particles, whereinthe particles have a mass median particle size of from about 300 toabout 800 μm.
 19. An absorbent core for acquiring, distributing andstoring body fluids, which comprises the absorbent member of claim 1.20. An absorbent article comprising a fluid pervious topsheet, abacksheet and the absorbent core of claim 19 positioned between saidtopsheet and said backsheet.
 21. The absorbent article of claim 26 whichis a diaper.
 22. The absorbent article of claim 26 which is a catamenialpad.
 23. The absorbent article of claim 26 which is a wound bandage. 24.The absorbent member of claim 1 wherein at least a portion of thehydrogel-forming absorbent polymer is in the form of fibers.
 25. Theabsorbent member of claim 24 wherein the region comprisinghydrogel-forming absorbent polymer comprises at least 10% by weightfibers and at least 40% by weight particles.
 26. An absorbent member forthe containment of aqueous body fluids, which comprises at least oneregion comprising hydrogel-forming absorbent polymer in a concentrationof from about 50 to 100% by weight, said hydrogel-forming absorbentpolymer having: (a) a Performance under Pressure (PUP) capacity value ofat least about 29 g/g under a confining pressure of 0.7 psi (5 kPa); (b)a Dynamic Gelling Rate (DGR) value of at least about 0.25 g/g/sec; and(c) when the hydrogel-forming absorbent polymer is in the form ofparticles, the mass median particle size is from about 300 to about 800μm.
 27. The absorbent member of claim 26 wherein the hydrogel-formingabsorbent polymer is in the form of unagglomerated particles.
 28. Theabsorbent member of claim 26 wherein said hydrogel-forming absorbentpolymer has a saline flow conductivity value of at least about 50×10⁻⁷cm³sec/g.
 29. The absorbent member of claim 28 wherein saidhydrogel-forming polymer has a SFC of at least about 75×10⁻⁷ cm³sec/g.30. The absorbent member of claim 26 wherein said hydrogel-formingabsorbent polymer has a Porosity of the Hydrogel Layer (PHL) of at leastabout 0.18.
 31. The absorbent member of claim 30 wherein saidhydrogel-forming absorbent polymer has a Porosity of the Hydrogel Layer(PHL) of at least about 0.25.
 32. The absorbent member of claim 26wherein said hydrogel-forming absorbent polymer has less than about 10%extractable polymer material.
 33. The absorbent member of claim 32wherein said hydrogel-forming absorbent polymer has less than about 7%extractable polymer material.
 34. The absorbent member of claim 26wherein said hydrogel-forming absorbent polymer has a gel volume of atleast about 35 g/g.
 35. The absorbent member of claim 34 wherein saidhydrogel-forming absorbent polymer has a gel volume of at least about 45g/g.
 36. The absorbent member of claim 26 wherein said hydrogel-formingabsorbent polymer has a gel strength of at least about 20,000 dynes/cm².37. The absorbent member of claim 26 wherein said hydrogel-formingabsorbent polymer is in the form of particles, and wherein the particleshave a mass median particle size of from about 350 to about 750 μm. 38.An absorbent core for acquiring, distributing and storing body fluids,which comprises the absorbent member of claim
 37. 39. The absorbentmember of claim 26 wherein the basis weight of said hydrogel-formingabsorbent polymer in said region is at least about 10 gsm.
 40. Theabsorbent member of claim 26 wherein said region comprises from about 70to 100% of said hydrogel-forming absorbent polymer.
 41. The absorbentmember of claim 40 wherein said region comprises from about 80 to 100%of said hydrogel-forming absorbent polymer.
 42. An absorbent core foracquiring, distributing and storing body fluids, which comprises theabsorbent member of claim
 26. 43. An absorbent core for acquiring,distributing and storing body fluids, which comprises a fluid storageabsorbent layer comprising fibrous matrix having at least one regioncontaining particles of a surface crosslinked hydrogel-forming absorbentpolymer having carboxy functional groups, said hydrogel-formingabsorbent polymer being present in said region in a concentration offrom about 50 to 100% by weight, said hydrogel-forming absorbent polymerproviding a gel continuous fluid transportation zone when in a swollenstate and having: (a) a Performance under Pressure (PUP) capacity valueof at least about 25 g/g under a confining pressure of 0.7 psi (5 kPa);(b) a Dynamic Gelling Rate (DGR) value of at least about 0.18 g/g/sec;(c) when the hydrogel-forming absorbent polymer is in the form ofparticles, the mass median particle size is at least about 100 μm; (d) aSaline Flow Conductivity (SFC) value of from about 30 to about 1000×10⁻⁷cm³sec/g; (e) about 15% or less extractable polymer material; and (f) agel volume of from about 25 to about 100 g/g.
 44. The absorbent core ofclaim 43 which further comprises a fluid acquisition layer.
 45. Theabsorbent core of claim 44 wherein said fluid acquisition layercomprises chemically stiffened cellulosic fibers.
 46. The absorbent coreof claim 43 wherein said storage layer comprises a layer of saidhydrogel-forming polymer contained between a first fibrous layer and asecond fibrous layer.
 47. The absorbent core of claim 46 wherein saidstorage layer is thermally bonded.
 48. The absorbent core of claim 43wherein said region comprises from about 70 to 100% of saidhydrogel-forming polymer.
 49. The absorbent core of claim 48 whereinsaid region comprises from about 80 to 100% of said hydrogel-formingpolymer.
 50. The absorbent core of claim 43 wherein the basis weight ofsaid hydrogel-forming absorbent polymer in said region is at least about50 gsm.
 51. The absorbent core of claim 43 wherein said hydrogel-forming:absorbent polymer is selected from the group consisting of: hydrolyzedstarch-acrylonitrile graft copolymers, partially neutralized hydrolyzedstarch-acrylonitrile graft copolymers, starch-acrylic acid graftcopolymers, partially neutralized starch-acrylic acid graft copolymers;saponified vinyl acetate-acrylic ester copolymers; hydrolyzedacrylonitrile copolymers; hydrolyzed acrylamide copolymers; slightlynetwork crosslinked products of any of the foregoing copolymers;partially neutralized polyacrylic acid; slightly network crosslinkedproducts of partially neutralized polyacrylic acid; and mixturesthereof.